Recent developments in ionic liquid electrolytes for cellulose or biomass dissolution has also allowed for high-resolution ¹H and ¹³C NMR on very high molecular weight cellulose. This permits the development of advanced liquid-state quantitative NMR methods for characterization of unsubstituted and low degree of substitution celluloses, for example, surface-modified nanocelluloses, which are insoluble in all molecular solvents. As such, we present the use of the tetrabutylphosphonium acetate ([P₄₄₄₄][OAc]):DMSO-d₆ electrolyte in the 1D and 2D NMR characterization of poly(methyl methacrylate) (PMMA)-grafted cellulose nanocrystals (CNCs). PMMA-g-CNCs was chosen as a difficult model to study, to illustrate the potential of the technique. The chemical shift range of [P₄₄₄₄][OAc] is completely upfield of the cellulose backbone signals, avoiding signal overlap. In addition, application of diffusion-editing for ¹H and HSQC was shown to be effective in the discrimination between PMMA polymer graft resonances and those from low molecular weight components arising from the solvent system. The bulk ratio of methyl methacrylate monomer to anhydroglucose unit was determined using a combination of HSQC and quantitative ¹³C NMR. After detachment and recovery of the PMMA grafts, through methanolysis, DOSY NMR was used to determine the average self-diffusion coefficient and, hence, molecular weight of the grafts compared to self-diffusion coefficients for PMMA GPC standards. This finally led to a calculation of both graft length and graft density using liquid-state NMR techniques. In addition, it was possible to discriminate between triads and tetrads, associated with PMMA tacticity, of the PMMA still attached to the CNCs (before methanolysis). CNC reducing end and sulfate half ester resonances, from sulfuric acid hydrolysis, were also assignable. Furthermore, other biopolymers, such as hemicelluloses and proteins (silk and wool), were found to be soluble in the electrolyte media, allowing for wider application of this method beyond just cellulose analytics.

The limited access to fast and facile general analytical methods for cellulosic and/or biocomposite materials currently stands as one of the main barriers for the progress of these disciplines. To that end, a diverse set of narrow analytical techniques are typically employed that often are time-consuming, costly, and/or not necessarily available on a daily basis for practitioners. Herein, we rigorously demonstrate a general quantitative NMR spectroscopic method for structural determination of crystalline cellulose samples. Our method relies on the use of a readily accessible ionic liquid electrolyte, tetrabutylphosphonium acetate ([P₄₄₄₄][OAc]):DMSO-d₆, for the direct dissolution of biopolymeric samples. We utilize a series of model compounds and apply now classical (nitroxyl-radical and periodate) oxidation reactions to cellulose samples, to allow for accurate resonance assignment, using 2D NMR. Quantitative heteronuclear single quantum correlation (HSQC) was applied in the analysis of key samples to assess its applicability as a high-resolution technique for following cellulose surface modification. Quantitation using HSQC was possible, but only after applying T₂correction to integral values. The comprehensive signal assignment of the diverse set of cellulosic species in this study constitutes a blueprint for the direct quantitative structural elucidation of crystalline lignocellulosic, in general, readily available solution-state NMR spectroscopy.Graphic